Mirror reflectors for fluorescent lamps



Jan. 9, 1968 H. SCHMITT 3,

MIRROR REFLECTORS FOR FLUORESCENT LAMPS Filed June 23, 1965 2 Sheets-Sheet 1 Fig.2 Fig.3

PRIOR ART INVENTOR: BY HF/A/R/Cb SCf/M/T T ATTORNEY Jan. 9, 1968 H, SCHWTT 3,363,093

MIRROR REFLEGTORS FOR FLUORESCENT LAMPS Filed June 23. 1965 k 2 Sheets-Sheet 2 United States Patent M 3,363,093 lVIIRROR REFLECTIORS FOR FLUORESCENT S Heinrich Schmitt, Wilhelm Leuschner Str. 87, Frankfurt am Main, Germany Filed June 23, 1965, Ser. No. 466,322 Claims priority, application Germany, June 25, 1964, Sch 35,378 4 Claims. (Cl. 240-4135) ABSTRACT OF THE DISCLOSURE In known mirror fixtures for fluorescent lamps of tubular shape, the mirror reflecting trough has a parabolic cross-section. The focal distance of the latter is almost equal to the radius of the fluorescent lamps cylinder. The distance between the reflector and the tube in the apex is substantially equal to the radius, so that the focal point of the parabola is disposed on or within the tube and on its vertical axis.

Due to the spacially spread out surface of the diffusion emitting fluorescent lamp, a clear corelation of the focal points, as in the case of a directed emission of a pointed light source, is not possible.

Mirror reflecting lamps of this type produce a narrow light band which reach a maximum near the axis of the reflector. With a side angle of about 15 the light intensity is already reduced about one-fifth and amounts to only the double of the bare fluorescent lamp at 30. At about a 45 side angle, the reflector becomes ineffective, so that with further angle openings only the bare fluorescent tube illuminates.

This fact may be the reason why the manufacturers of mirror reflector lamps have arranged two or even three fluorescent light tubes directly behind one another, whereby the focal distances of the common reflector parabolas and correspondingly their opening distances are increased about one-third. At the same time it is anticipated that only the foremost tube will be directly effective in the direction of the axis. A coordination of two or even three directly mounted, successive fluorescent light tubes with the focal point of a common larger parabola, appears even less possible, according to the laws of reflection. The angle of radiation is actually widened, yet the degree of effectiveness may not be in favorable relationship to the doubled or multiplied :use and expenditure of energy and material, as is apparent from a study of light division curves. The foremost fluorescent light tube covers not only the one lying behind it but both obstruct part of the otherwise eflective reflector in side angles and only partial sections of the surface are capable of reflecting.

The above-mentioned disadvantages are obviated by the invention and there is achieved in particular a retention of the wide band due to the novel construction of the mirror reflector, contrary to the known teaching in the art.

Instead of a mirror reflector trough with a parabolic cross-section, the cross-section according to the invention comprises two partial parabolas. These partial parabolas, when assembled, have only about half the focal length of the heretofore focal length of a fluorescent light tube. The axes of illuminations of these partial parabolas extend 3,363,093 Patented Jan. 9, 1968 laterally. The main axis of the light is spaced about onehalf the radius of the fluorescent lamp tube and the crosssection point of the partial parabolas are disposed on the main axis about the zenith of the fluorescent lamp tube or within said tube. The focal points of the parial parabolas may be disposed laterally of the main axis or within the fluorescent lamp cylinder.

The side wings of the middle reflecting troughs can extend a distance of about one-half of the radius under the fluorescent light tube. In this case the opening distance corresponds to the circumference of the cylinder tube, so that the total surface thereof may be employed for reflection purposes.

A mirror reflector of this type, for fluorescent lamp tubes produces a light band which has about 3.14 times the light intensity of a bare tube in the direction of the main axis, yet in contrast to the known reflectors has a double light intensity at side angle of 45 In contrast to prior mirror reflecting lamps there are no dead reflection Zones for equal opening angles because the heretofore unused part of the surface of the fluorescent light tube, which is adjacent to the apex of the reflector, reflects partially directly into space through the lateral displacement of the partial parabolas and partly on the equal sides of the outer reflector wings and therefrom further into the free space.

In the drawing there is illustrated an embodiment example of the mirror reflector for a fluorescent light according to the invention idea, as compared with a known parabolic reflector.

In the drawing:

FIG. 1 is a schematic cross-section of both reflector members and a cross-section through the fluorescent light tube;

FIG. 2 is a schematically shown side reflection of a known parabola reflector;

FIG. 3 illustrates the lateral reflection of a reflector according to the invention, in comparason with a known reflector and FIG. 4 shows the comparative cross-section of FIG. 1, with the course of radiation and reflection drawn in.

The fluorescent light tube is indicated by the numeral 1 in FIG. 1. The known parabolic reflector member 2, is indicated by dotted lines and the reflector trough by numeral 3 and consisting of two partially parabolic cross-sections 3 and 3 The reference character S indicates the apex of the known parabola, while S and S the apices of the partial parabolas. F is the focal point of the known parabola and F and F are the focal points of the partial parabol-as. H is the focal axis of the known parabola-s and at the same time the main axis of lamp 1, H and H are the focal axes of the partial parabolas and r the radius of the fluorescent lamp tube.

It will be apparent that the reflector member according to the invention is disposed with the joining edges between the two partial parabolas on the fluorescent light tube 1, in its apex line. The apex points S and S of both partial parabolas 3 and 3 are disposed at a distance of less than r from the cylindrical surface on the fluorescent lamp tube. Both focal points F and F are disposed interiorly of fluorescent light tube 1.

In order to illustrate the novel mode of operation of the reflector construction according to the invention, the course of rays for various boundary rays is shown in FIG- URE 4, for a simple parabolic reflector on the left and for the right hand trough of the biparabolic reflector according to the invention of the right.

Since the invention relates to diffused light, limiting rays, normal rays and tangential rays are shown by way of illustration. Normal rays are understood to mean those rays which emerge perpendicularly from a point on the lamp surface as if they originated from its centre axis.

3 Tangential rays are those which emerge tangentially from luminous points on the surface.

The normal rays will be discussed first. In the simple parabolic reflector 2 (left), the focal ray MP is reflected back into itself and remains ineffective in space. The rays M8 and MP are reflected at 4 and 5 respectively back onto the surface of the lamp at 6 and 7, respectively and again remain ineffective in space. There is thus absent special reflection for all normal rays substantially in the upper third of the region of the reflector 2 adjacent to the lamp.

In the biparabolic construction according to the invention, on the other hand, the comparable rays M5 and MF are reflected on the partial parabolic reflector 3 into the room past the fluorescent lamp 1. For reflection points between S and F, as shown at the normal ray MN, wherein a reflection first occurs at the tangential rays, which are shown in broken lines, the following conditions apply:

With the simple parabolic reflector 2 (left), the tangential ray F is reflected at 8, substantially parallel to the main axis H, into the room. On the other hand, the tangential ray associated with the normal ray MP is not reflected at all. The behaviour is similar for a transverse ray at the lowest point U of the fluorescent lamp.

With the biparabolic construction, the tangential ray through F is first reflected to R on the reflector and then into the room. The tangential ray associated with the normal ray MF is reflected at R on the reflector and from there into the room. Likewise the transverse ray at the lowest point U of the fluorescent lamp which is reflected into the room at R The comparison shows that with the biparabolic reflector according to the invention, in contrast to the simple parabolic reflector, various points of the surface of the fluorescent lamp are spacially effective simultaneously as a result of the overlapping and superimposition of direct reflection and indirect reflection in the same directions of radiation so that the reflector has a higher light intensity than the bare lamp.

The practical result is compared in FIGURES 2 and 3. The hatched lines show the light bands emerging from the light fitting.

With the simple reflector shown in FIGURE 2, dead reflection zones appear at the outer edges of the reflector at a lateral angle of about 30. At a lateral angle of about 45 the reflector is completely ineffective and has only dead reflection zones.

In the biparabolic reflector of FIGURE 3, fluorescent lamp'and reflector form closed light bands for the whole width of opening of the reflector at the same lateral angles. Only at even greater lateral angles do similar dead reflection zones appear rising from the outer edges while at the same opposite reflector edges gradually hide the fluorescent lamp.

The considerably increased luminous effect in the portion of space provided for the emergence of light is apparent from the above.

The reflectors according to the invention may appropriately be produced from plastic materials which are provided with a metallized reflection layer instead of the former glass mirror construction,

The use of plastic materials not only simplifies and reduces the cost of productiombut enables such mirror reflectors to be constructed in the form of attachments with which existing installations can be equipped subsequently, as a result of the considerable reduction in weight. For this purpose, the reflectors may have incisions of excisions,

for example of the width and depth of the holders and posthe heretofore employed glass mirrors, and such materials may be provided with a metalized reflecting shield.

The employment of synthetic materials not only simplifies and cheapens production, but also permits, through a substantial reduction in weight, the construction of such a mirror reflectors as mounting devices with which available installations may be outfitted. For this purpose the refiectors may have cutouts or recesses, and may be provided with sockets and starters, so that the reflectors may be held by a simple placing of these on the fluorescent light tubes and may be secured against rotation.

What I claim is:

1. A mirror reflector for elongated fluorescent lamps having a form which, in cross-section, comprises two adjacent partial parabolas and is adapted to fit on the top line of a fluorescent lamp having a circular cross-section and envelop the top and the sides of the lamp, the two focal axes of the parabolas extending through the surface of the fluorescent lamp laterally of a vertical plane through the main axis of the fluorescent lamp and parallel therewith, the two focal points of the component parabolas lying in the fluorescent lamp.

2. A mirror reflector as claimed in claim 1, wherein the tWo reflector parabola troughs merge directly into one another.

3. A mirror reflector as claimed in claim 1, further comprising a concave wall intermediate said partial parabolas, said parabolas merging with said concave Walls.

4. A mirror reflector as claimed in claim 1, wherein the focal length of the component parabolas and the distance of their focal axes from the main axis of the light source corresponds substantially to half the size of the radius of the cross-section of the light source.

References Cited UNITED STATES PATENTS 2,188,129 1/1940 Ayotte 240-10.69 2,194,841 3/ 1940 Welch 24011.4 2,232,499 2/ 1941 Waterbury 24051.11 2,330,924 10/ 1943 Rolph 240-5111 2,337,437 12/ 1943 Allen 240-51.11

FOREIGN PATENTS 73 0,860 6/ 1955 Great Britain.

NORTON ANSHER, Primq'ry Examiner.

RICHARD M. SHEER, Assistant Examiner. 

